Shaft mounted eddy current drive

ABSTRACT

A drive has a hub with first and second end portions and a shoulder located thereon. An armature and sheave assembly is located on bearings on the hub first end portion. The armature forms a cavity for receiving an electromagnet, which abuts against the shoulder. Slip rings are coupled to the electromagnet by way of a fan and a slip ring shaft. The slip rings, which are adjacent to the second end of the hub, can be of a small diameter to extend brush life. In addition, the same size slip rings can be used on different sizes of the drive. Two piece brush holders are provided for each brush. Each brush holder can be disassembled into its respective pieces for cleaning. The brush holders and slip rings can be protected from the environment by a cover.

FIELD OF THE INVENTION

The present invention relates to variable speed drives that are mountedonto an output shaft of a motor, such as a fixed speed electric motor,and in particular the present invention relates to eddy current drives.

BACKGROUND OF THE INVENTION

There are many applications where it is desirable to have a fixed speedmotor provide a variable speed output. For example, in ventilationsystems, an ac synchronous motor is used to rotate an air mover, such asa fan. The energy efficiency of this system increases if the speed ofthe motor remains fixed while the speed delivered to the fan can bevaried.

In the prior art, there are variable speed drives that mount onto theoutput shaft of the motor. Around the outer circumference of the driveare one or more sheaves. The sheaves receive belts that are coupled to aload. The drive permits a controlled amount of slip. At zero slip, thefull rotary power of the motor output shaft is applied to rotate thesheaves. At full slip, the output shaft continues to rotate, but thesheaves remain stationary under a load. Thus, at zero slip, the fullyrotary power of the motor is applied to the load, while at zero slip, norotary power is applied to the load.

In Albrecht et al., U.S. Pat. No. 4,400,638, there is disclosed a shaftmounted eddy current drive. The amount of slip is controlledelectrically using eddy currents. The output sheaves are mechanicallycoupled to poles of an electric coil. There are provided opposite,interdigitated poles. An armature provides a magnetic path between theopposite poles. The armature is mechanically coupled to the output shaftof the electric motor. As the motor shaft rotates, the armature alsorotates at the same speed as the shaft. In order to rotate the sheaves,current is applied to the coil. This creates an electromagnetic couplingbetween the poles and the armature, wherein the armature causes thepoles and the associated sheaves to rotate.

It is desired to improve upon the prior art drives. The slip rings ofthe Albrecht et al. drive have the same diameter as, and are locatedadjacent to, the sheaves. One disadvantage of the slip ring arrangementis the wear on brushes. The chief complaint among customers who buy theprior art drives is brush wear. The brushes must be frequently replaced,adding to the maintenance cost of the drives. The larger thecircumference of the slip rings, the shorter the life of the brushesbecomes because for each revolution of the motor, the brushes are infrictional contact with a long length of the slip rings.

Another disadvantage of the slip ring arrangement of Albrecht et al. isthat as the drive is sized larger or smaller for respective larger orsmaller load applications, the circumference of the slip rings change.Thus, the slip rings must be custom made for each size drive. It isdesirable to make the slip rings a more uniform size, regardless of thesize of the drive, in order to manufacture and repair the drives moreefficiently.

Still another disadvantage of the slip ring arrangement of Albrecht etal. is the difficulty in protecting the slip rings and brushes from theenvironment. If the drive is used outside, it is subjected to moisture,which can reduce the life of the brushes.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a shaft mounted eddycurrent drive that has prolonged brush life.

Another object of the present invention is to provide a drive designthat uses the same size slip rings regardless of the power requirementsof the drive.

Still another object of the present invention is to provide a drive thatprotects the slip rings and brushes from the environment.

The drive of the present invention includes a hub that is structured andarranged to be coupled to a motor shaft. The hub has a shoulder, whichshoulder is coupled to the hub. An electromagnet is mounted on the huband abuts against the shoulder. The electromagnet is rotatably coupledto the hub. There is a driven member that is mounted to the hub bybearings. The driven member has a load portion and an armature, with theload portion being structured and arranged to be rotatably coupled to aload and the armature being located adjacent to the electromagnet.

The drive of the present invention has several advantages over prior artdrives. One advantage is due to the design of the slip rings. The sliprings are located at the outer end of the drive and are of relativelysmall diameter. In the preferred embodiment, a slip ring shaft providesa support for mounting the slip rings. The small diameter of the sliprings greatly prolongs brush life by presenting a relatively smallcircumference that the brushes must traverse for each revolution of theslip rings. Because the brushes contact shorter lengths of slip ringsper revolution, the lives of the brushes are prolonged.

Also, by providing the slip rings on a separate slip ring shaft, thesize of the slip rings is independent of the sizes of the motor shaft,the sheave and the drive in general. Thus, as the design of the drive isenlarged to provide a drive with more horsepower, or reduced to providea drive with less horsepower, the size of the slip rings, and thus thebrush holders, can remain the same. This uniformity in size of sliprings, which is independent of the size of the drive, reducesmanufacturing costs while allowing flexibility in producing a productline of plural drives, each of which is designed for a specifichorsepower. Inventory costs are reduced as well, because bothmanufacturer and user need only stock one size of slip rings and brushholders.

The drive also provides a housing or cover for containing and protectingthe slip rings and brushes from the elements. This is important fordrives that are used outside, as brush life is extended. The coverprevents moisture from contacting the brushes and the slip rings.

The design of the drive allows for easy partial disassembly whilemaintaining the connection of the drive to the load and to the motorshaft. The brush holders, slip rings, fan and electromagnet can beremoved while leaving the hub connected to the motor shaft and thesheaves coupled to the load. This reduces maintenance time because thedrive does not have to be completely removed during disassembly.

The drive is more stable in operation because the sheaves are fullymounted on bearings and are located closer to the end of the hub thatcouples to the end of the motor. Prior art drives mount the brush holderbracket on the same end of the hub as the sheaves. This causes thesheaves to either be mounted further from the motor (which unfavorablyloads the motor shaft and produces vibration) or to be only partiallymounted onto a bearing (which produces unbalancing and vibration of thesheaves). The drive of the present invention does not suffer these priorart problems because the sheaves are fully supported by the bearings. Inaddition, the sheaves, as well as the bulk of the mass of the driver,are located closer to the motor than the prior art drives. Thisdrastically reduces the overhung load on the motor shaft, prolongingmotor life.

Another advantage of the drive of the present invention is that thesheaves are fully exposed at all times. In the prior art, the brushholder bracket extends across the sheaves. With the drive of the presentinvention, the slip rings and brush holder bracket are located on theopposite end of the drive from the sheaves. Thus, the belts can beinstalled onto and removed from the sheaves without removing the brushholder bracket. In addition, a conduit is used to prevent rotation ofthe brush holder bracket. The conduit is anchored to the motor andextends through the belts. This arrangement allows the belts to beinstalled and removed without disassembling any part of the drive.

Still another advantage of the drive is the coupling of theelectromagnet to the hub and the fan to the electromagnet. The motorshaft rotates the hub, the electromagnet and the fan continuously atmotor speed. This continuous movement of the electromagnet and the fanproduces continuous cooling of the electromagnet. Prior art driveslocate the electromagnet on the driven member, which may be stationaryor operating at a low speed. The electromagnet on prior art drives isnot cooled as effectively as with the present invention due to thereduced rotational speed. Effective cooling of the electromagnetprolongs the life of the electromagnet.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cross sectional side view of the shaft mounted eddycurrent drive of the present invention, in accordance with a preferredembodiment.

FIG. 2 is a view showing the outer end of the drive, with a housingaround the slip rings and brush holder partially cut away.

FIGS. 3 and 5 are side views showing the interiors of the first andsecond portions, respectively, of a brush holder, in accordance with apreferred embodiment.

FIG. 4 is an end view showing how the first and second portions of thebrush holder fit together.

FIG. 6 is a top plan view of the brush holders.

FIG. 7 is a cross-sectional view taken along lines VII--VII of FIG. 6.

FIG. 8 is a side view of the first portion of a brush holder, with abrush installed, and the second portion removed for clarity.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIG. 1, there is shown a partial cross sectional side view of thedrive 11 of the present invention, in accordance with a preferredembodiment. The drive 11 has a shaft mounted portion and a load portion.The shaft mounted portion includes a hub 13, pole pieces 15 and a coil17. The shaft mounted portion mounts onto the shaft of a motor and isrotated directly by the motor shaft. The load portion is rotated by anelectromagnetic field developed by the shaft mounted portion. The loadportion is coupled to the load (e.g. a fan) and includes an armature 19and sheaves 21. In addition, the drive includes slip rings 23, a brushholder bracket 25 and brush holders 27.

The shaft mounted portion will now be described. The hub 13 is generallyin the form of a sleeve. The hub 13 has a cylindrical cavity 29 locatedtherein for receiving a shaft 31 of a motor 33. The hub 13 is coupled tothe shaft 31 by a conventional and commercially available compressiontype shrink disk (not shown). Alternatively, the cavity 29 may be keyedor threaded to receive respective keys or threads on the motor shaft.The hub 13 has an outer end portion and an inner end portion (with innerbeing referenced as closer to the motor and outer being referenced asfurther from the motor 33).

Mounted on the outer end portion of the hub are the pole pieces 15.There are two pole pieces, an inner piece and an outer piece. Each polepiece 15 is made up of an annular portion 35, with poles 37 extendingfrom the outer diameter of the annular portion and a lip 39 extendingfrom the inner diameter of the annular portion. The poles 37 on anindividual pole piece are spaced apart by gaps. When the pole pieces areassembled as shown, the poles from the inner and outer pole pieces areinterdigitated so as to form alternating polarities around thecircumference of the assembly of pole pieces. The assembled pole pieces15 encircle the coil 17 of wire. Thus, the coil 17 is encircled by theannular portions 35, lips 39 and poles 37 of the pole pieces. The polepieces and the coil extend around the circumference of the hub. The polepieces 15, and thus the encircled coils, are secured to the hub 13 bybolts 41. The hub 13 has a circumferential shoulder 43 that extendsradially outward to receive the bolts and to position the pole pieces15. The pole pieces abut against the shoulder 43.

The load portion will now be described. The sheaves 21 are mounted tothe hub 13 by way of bearings 45. In the preferred embodiment, thebearing 45 is a double row ball bearing. Alternatively, the bearing maybe two bearings. The bearings 45 are located on the hub between theshoulder 43 and a snap ring 47 that is on the hub. The bearings 45extend around the circumference of the hub. The sheaves 21 are locatedaround the outer circumference of the bearings. The sheaves 21 arepositioned on the bearings by a shoulder 49 on one end and bolts 51 onthe other end. The sheaves receive belts 22, which are rotatably coupledto a load such as a fan.

The armature 19 is coupled to the sheaves by a radially extending wall53. The armature 19 is a hollow cylinder and is made of a material thatis high in conductivity and permeability. The wall has openings 55therethrough that communicate with a cavity 56 formed by the armature 19and the wall 53. The cavity 56 receives the pole pieces 15. The openings55 allow air circulation through the pole pieces. The sheaves 21,armature 19 and wall 53 form an integral assembly. Alternatively, aninterior sleeve can be press fit into the inside diameter of thearmature. The interior sleeve can be made of a material that is suitablefor the production of eddy currents (high conductivity, highpermeability) while the armature around the sleeve can be designed todissipate heat.

The slip rings 23 are secured to the pole pieces 15 by way of a fan 57.The fan 57 is located so that the pole pieces 15 are interposed betweenthe fan 57 and the sheaves 21. Bolts 59 secure the fan 57 to the outerpole piece 15. The fan has openings 61 therein so that as the polepieces rotate, the fan causes air to circulate through the openings 55,61 and the pole pieces for cooling.

A slip ring shaft 63 is coupled to the fan 57 by bolts 65. The slip ringshaft 63 extends in an axial direction away from the sheaves 21. Theslip ring shaft has first and second outer surfaces 67, 69. The firstouter surface 67 is located at the outer end of the slip ring shaft. Theslip rings 23 are mounted on the first surface 67 with a key 71 and anend plate 73. The end plate 73 is bolted onto the outer end of the slipring shaft. The slip rings 23 extend around the circumference of theslip ring shaft. Wires 75 connect the slip rings 23 to the coil 17. Thewires 75 extend through passageways 76 drilled or otherwise formed inthe slip ring shaft 63 and the fan 57.

The brush holder bracket 25 has a sleeve portion 77 that is mountedaround the second surface 69 of the slip ring shaft 63 by way of abearing 79. The bearing 79 is secured in place against a shoulder on thefan 57 and snap rings. The bracket 25 has a radial extension portion 81that extends past the armature 19.

The brush holders 27 are coupled to the radial extension portion 81 ofthe brush holder bracket 25. Referring to FIGS. 3-8, there are two brushholders 27, one for each brush 85. Each brush holder 27 has a firstportion 82 (shown in FIG. 3) and a second portion 83 (shown in FIG. 5).The first portion 82 is provided with pins 84 on its interior surface,while the second portion 83 is provided with holes 86 for receiving thepins 84. The two portions 82, 83 snap fit together with the pins 84inserted into the holes 86 (see FIG. 4). Each portion has a groovelocated therein. When the portions are assembled, the groove forms agenerally rectangularly shaped cavity 87 for receiving the carbonbrushes 85 (see FIGS. 6 and 8). Each side wall of the cavity 87 has ashallow groove 88 that allows the brushes to move inside the cavity.

Each brush 85 is connected to a contact 94 by a flexible wire 92. Aspring 89 is interposed between the brush 85 and the contact 94. Thecontact 94 has edges that bear on a top surface 94A of the assembledbrush holder 27. Thus, the brush 85 is prevented from being pulled outfrom the bottom 94B of the brush holder. A clip 91 overlies the contact94. The clip is L-shaped to provide a connection point for a wire 91A.The wires 91A connected to the clips are routed to an external powersource by a conduit 93. The clip 91 is secured to the brush holder by ascrew 92A. The clip is located inside of a recess 91B on the top of thebrush holder. This recess 91B locates the clip 91, and the connectionpoint with the wire 91A entirely within the protective confines of thebrush holder. The contact 94 makes electrical contact with the clip 91.

The two brush holders 27 are oriented with respect to each other asshown in FIG. 6, so that the clips, when installed, face oppositedirections. This simplifies the wire connections with the clips. Thebrush holders are bolted to the brush holder bracket by bolts that arereceived by holes 95. Referring to FIG. 2, the brush holders 27 arelocated close to the slip rings 23 so that the brushes 85, whichprotrude out of the cavities, can contact the slip rings.

The brush holder bracket 25 has end walls 97 that extend in an axialdirection. The end walls receive a housing 99 or cover, a portion ofwhich has been broken away in FIGS. 1 and 2 to more clearly illustratethe slip rings and brush holders. The housing 99 and the bracket 25completely encase the slip rings 23 and the brush holders 27 so as toprotect the slip rings and brush holders from the environment andmoisture, thereby extending the life of the brushes. Screws are used tocouple the housing to the bracket 25. The housing is removable to allowaccess to the slip rings and brush holders.

The brush holder bracket 25 has an extension 101 (see FIG. 1) that isused to position a speed sensor 103 adjacent to the rotating armature.The outer surface of the armature 19 is scored at regular intervals (seeFIG 2). In the preferred embodiment, the scoring takes the form ofgrooves 105 which form peaks 107. The sensor 103 is a magnetic pulsepickup. Thus, as the steel armature 19 rotates, every peak 107 iscounted. Conventional control circuitry, not shown, is used to monitorthe signal produced by the sensor and to control the amount of currentsupplied to the brush in order to control the speed of the armaturerotation.

The drive need not be supplied with a speed sensor. Many applicationsalready have control systems. For example, in HVAC, inputs oftemperature and pressure are used to control the speed of the armaturerotation.

The assembly of the drive will now be described, referring to FIG. 1.The bearings 45 are installed and secured onto the hub 13. Then, thearmature and sheave assembly 19, 21 are installed and secured onto thebearings 45. The pole pieces 15 and coil 17 are assembled together tomake up an annular electromagnet. The pole pieces 15 and coil 17 areinstalled onto the hub 13 with the pole pieces in abutting relationshipwith the shoulder 43. The pole pieces are then bolted 41 in place. Thefan 57 and the slip ring shaft 63 are bolted 65 together. The fanassembly is bolted 59 to the pole pieces. The center 111 of the fan isdisk shaped and received by the hub cavity 29 to center the fan withrespect to the pole pieces. The support bracket 25 is then mounted, byway of bearings 79, to the slip ring shaft. Then, the brush holders 27and speed sensor 103 are coupled to the bracket 25.

The drive 11 is then installed onto a motor shaft 31. The motor shaft 31is inserted into the hub cavity 29 and a compression disk is used tofirmly secure the hub to the shaft. The cover 99 is installed onto thebracket 25.

The conduit 93, which contains the wires connected to the brushes, isanchored to a fixed platform, such as the motor 33. A bracket 33A isused to couple the conduit 93 to the motor 33. The wires from the speedsensor 103 are typically tie wrapped to the outside of the conduit 93.

In the preferred embodiment, the conduit 93 is positioned between thesheaves 21 and the load. Thus, when the belts are installed on thesheaves, the conduit 93 extends through the loops formed by the belts;that is the belts 22 extend around both the sheaves 21 and the conduit93. This arrangement of the conduit 93 through the belts 22, togetherwith the arrangement of the slip rings and the bracket on the outer endof the drive, away from the sheaves, allows the belts to be installedand removed from the sheaves and the load, without disconnecting theconduit and without removing the bracket 25 and the brush holders 27.Thus, the belts can be quickly installed or removed without disturbingthe drive, thereby reducing maintenance and down times.

The sheaves 21 are fully supported by the bearings 45, thereby providinglong operational life of the sheaves and bearings 45. In addition, thesheaves and the bulk of the mass (the electromagnet) are located closeto the motor 33. This arrangement reduces the overhung load on the motorshaft.

The operation of the drive 11 will now be described. The motor 33 isstarted and the shaft 31 is rotated. As the shaft rotates, it rotatesthe pole pieces 15 and the coil 17. The sheaves 21 do not rotate, asthey are held stationary by the load.

To rotate the sheaves, a selected amount of current is provided to thecoil, by way of the brushes and slip rings. This energizes the coil,which causes an electromagnetic field to be developed between adjacentpoles. The armature becomes electromagnetically coupled to the polepieces, wherein the armature and the sheaves are rotated. If theelectromagnetic field is weak, then there will be some slip between thearmature and the pole pieces. Thus, for every revolution of the polepieces, the armature will rotate less than one revolution. Bycontrolling the strength of the energizing current to the coil, theamount of slippage and the speed of the armature can be controlled.

The drive 11 may be partially disassembled for maintenance andinspection purposes without uncoupling the drive from the load. Thus,the belts may be retained on the sheaves 21 during partial disassembly.To partially disassemble the drive 11, the bolts 59 are removed, therebyallowing the fan 57, slip ring shaft 63 and bracket 25 to be removedfrom the pole pieces 15. Then, the bolts 41 are removed, therebyallowing the pole pieces 15 and coil 17 to be removed from the interiorcavity 56 of the armature 19. The electromagnet (the pole pieces and thecoil) and the slip ring arrangement can be worked on and thenreinstalled. During the partial disassembly of the drive, the hub 13 andarmature-sheave assembly 19, 21 remain coupled to the motor shaft and tothe load. Thus, the design of the drive simplifies maintenance andinspection procedures.

Replacing the brushes 85 is also simple. One method involves removingthe clip 91 (see FIG. 8). The contact 94 and brush 85 are then removedand replaced, and the clip 91 is reinstalled. Thus, the brush holders 27remain coupled to the bracket 25. Another method of changing the brushesinvolves removing and disassembling the brush holders 27 into theirfirst and second portions 82, 83. This procedure allows the brushholders to be cleaned of carbon dust. After cleaning, the brush holdersare reassembled and new brushes are installed.

Replacement of the slip rings 23 is also simplified, requiring onlyremoval of the end plate 73, slipping the slip rings off of the shaft 63and reinstalling a new pair. Replacement of the brushes and slip ringscan be performed while leaving the drive intact on the motor shaft 31.

The foregoing disclosure and the showings made in the drawings aremerely illustrative of the principles of this invention and are not tobe interpreted in a limiting sense.

I claim:
 1. A variable speed drive, comprising:a) a hub that isstructured and arranged to be coupled to a motor shaft, said hub havinga shoulder that is directly coupled to said hub said shoulder extendingin a direction that is transverse to an axis of rotation of said hub; b)an electromagnet mounted on said hub and abutting against said shoulder,said electromagnet being directly coupled to said hub so as to rotate inunison with said hub; c) a driven member mounted to said hub bybearings, said driven member having a load portion and an armature, saidload portion being structured and arranged to be rotatably coupled to aload, said armature being located adjacent to said electromagnet.
 2. Avariable speed drive, comprising:a) a hub that is structured andarranged to be coupled to a motor shaft, said hub having a shoulder thatis coupled to said hub; b) an electromagnet mounted on said hub andabutting against said shoulder, said electromagnet being coupled to saidhub; c) a driven member mounted to said hub by bearings, said drivenmember having a load portion and an armature, said load portion beingstructured and arranged to be rotatably coupled to a load, said armaturebeing located adjacent to said electromagnet; d) first and second endson said hub, with said first end receiving said motor shaft; e) sliprings located adjacent to said hub second end, said slip rings beingelectrically coupled to said electromagnet.
 3. The drive of claim 2wherein said slip rings have a diameter that is smaller than a diameterof said load portion.
 4. The drive of claim 2 further comprising a slipring support coupled to said electromagnet, said slip ring supportextending away from said hub second end, said slip rings being locatedon said slip ring support.
 5. The drive of claim 4 further comprising:a)a brush holder support mounted to said slip ring support by bearings; b)brush holders coupled to said brush holder support and positionedadjacent to said slip rings.
 6. The drive of claim 5 further comprisinga speed sensor coupled to said brush holder support and positionedadjacent to said armature.
 7. The drive of claim 5 further comprising ahousing coupled to said brush holder support and encompassing said sliprings and said brush holders.
 8. The drive of claim 5 wherein said brushholders comprise first and second portions, with each portion having agroove, said respective groove being aligned with each other so as toform a cavity when said first and second portions are assembledtogether, said cavity receiving a brush.
 9. The drive of claim 5,wherein said load portion is located adjacent to said first end of saidhub, further comprising:a) a belt extending around said load portion soas to form a loop; b) means for anchoring said support bracket, saidanchoring means extending through said belt loop.
 10. The drive of claim5 further comprising a fan coupled to said electromagnet.
 11. A variablespeed drive, comprising:a) a hub that is structured and arranged to becoupled to a motor shaft, said hub having a shoulder that is coupled tosaid hub; b) an electromagnet mounted on said hub and abutting againstsaid shoulder said electromagnet being coupled to said hub; c) a drivenmember mounted to said hub by bearings, said driven member having a loadportion and an armature, said load portion being structured and arrangedto be rotatably coupled to a load said armature being located adjacentto said electromagnet; d) a fan coupled to said electromagnet.
 12. Avariable speed drive, comprising:a first rotatable member that comprisespole pieces and a drive coil; a second rotatable member that comprisesan armature; one of said first rotatable member or said second rotatablemember comprising a hub, the other of said first rotatable member orsaid second rotatable member being structured and arranged to be coupledto a load; said pole pieces having plural interdigitated poles, saidpoles being separated from said armature by a gap; said drive coillocated adjacent to said pole pieces, said pole pieces providing a pathfor a magnetic field produced by said drive coil; said hub having firstand second ends, said hub first end having an opening for receiving amotor shaft, said hub being structured and arranged to rotate about anaxis of rotation; a shaft that is coupled to said first rotatablemember, said shaft located adjacent to said hub second end, said shaftbeing structured and arranged to rotate about said axis of rotation; arotating conductor coupled to said shaft, said rotating conductor beingelectrically coupled to said drive coil; a stationary conductorrotatably coupled to said shaft, said stationary conductor beingelectrically coupled to said rotating conductor and being stationaryrelative to said rotating conductor.
 13. The variable speed drive ofclaim 12, further comprising:a support rotatably coupled to said shaft;a speed sensor coupled to said support, said speed sensor locatedadjacent to said other of said first rotatable member or said secondrotatable member that is structured and arranged to be coupled to saidload; means for maintaining said support stationary with respect to saidshaft.